1. Field of the Invention
The present invention relates to an automatically switchable sprinkler head for automatically discharging fire extinguishing water by opening a valve against the surrounding temperature rise by a fire and automatically ceasing the water discharge by closing the valve against the surrounding temperature drop by the extinguishment of the fire.
2. Description of the Related Art
In conventional sprinkler heads, the channel connecting the water supply opening of the head connecting part for the fire extinguishing pipe and the water discharge opening at the tip of the head is sealed by a heat sensitive material, which is melted by the heat of the fire, such as a fusible alloy. When the temperature is raised over a predetermined temperature by a fire, the heat sensitive material is melted so that the channel is opened for discharging water.
Therefore, once the channel is opened by the drive of the sprinkler head by the hot air in the fire, the water discharge continues even after the extinguishment of the fire until the water supply from the water source is finished, or the valve is closed manually by a clerk, who confirms the site so that the damage by the water discharge has been considerable.
Accordingly, a sprinkler head, which opens the valve by the temperature rise by a fire so as to automatically discharges water and closes the valve by the temperature drop by the extinguishment of the fire so as to automatically ceases the water discharge, using a bimetal or a shape-memory alloy has been proposed.
Specifically, U.S. Pat. No. 4,553,602, Japanese Unexamined Patent Publication No. 53-48397, and Japanese Unexamined Utility Model Publication No. 54-131800 (based on the priority claim: U.S. Application No. 196641 filed on Nov. 8, 1971) disclose a sprinkler head utilizing a bimetal.
Further, Japanese Unexamined patent Publication No. 60-249978 (based on the priority claim: U.S. application No. 605201 filed on Apr. 30, 1984) and Japanese Unexamined Patent Publication No. 5-123419 disclose a sprinkler head utilizing a shape-memory alloy.
In such a conventional sprinkler head, when the surrounding of the sprinkler head has an ordinary temperature, the bimetal or the shape-memory alloy is maintained in the ordinary temperature shape. In this state, the water discharging path inside the sprinkler head is kept in the closed state directly by the bimetal or the shape-memory alloy in the ordinary temperature state or indirectly via an optional element. When the temperature surrounding the sprinkler head is higher than a predetermined operating temperature, the bimetal deforms into a high temperature shape, or the shape-memory alloy restores the memorized shape. At the time, the water discharging path is opened by the deformed bimetal or restored shape-memory alloy so that the water discharging operation is initiated. Further, when the surrounding of the sprinkler head regains an ordinary temperature after the extinguishment of the fire by the water discharge, the bimetal or the shape-memory alloy deforms to the ordinary temperature shape so as to close the water discharging path.
In summary, in the conventional sprinkler heads, the water discharging path is opened by the bimetal deformation or the restoration of the shape-memory alloy caused by a temperature higher than a predetermined operating temperature.
However, a problem is involved in the bimetal corrosion. That is, the expected deformation cannot be achieved even at the predetermined operating temperature due to the bimetal corrosion so that the sprinkler head cannot be operated.
Further, since the temperature at which a bimetal deforms or a shape-memory alloy restores can be defined only in a range within several ten degrees so that the temperature at which the deformation or the restoration takes place cannot be pinpointed in the range. Therefore, the temperature at which the water discharging path is opened, that is, the sprinkler head starts the operation cannot be determined accurately. For the same reason, when the water discharging path is closed after the water discharge, the temperature at which the water discharging path is closed, that is, the operation of the sprinkler head is ceased cannot be determined accurately. Hence it has been difficult to accurately operate a conventional sprinkler head.
Moreover, in the conventional sprinkler heads, the water discharge is controlled only by the bimetal or the shape-memory alloy as mentioned above. Therefore, in order to discharge water at a predetermined water discharging temperature, a shape-memory alloy needs to be produced and assembled such that it can be immediately restored when the surrounding temperature reaches the water discharging temperature. However, as mentioned above, since the temperature at which a shape-memory alloy restores can be defined only in a range within several ten degrees, and due to the production difficulty of a shape-memory alloy, which can immediately restore at a predetermined temperature and generation of a production error, adjustment of each sprinkler head in assembly has been required. This makes the sprinkler head inefficient, and deteriorates the mass-productivity.
The above-mentioned problems will be explained more specifically with reference to an automatically switchable sprinkler head using a shape-memory alloy disclosed in Japanese Unexamined Patent Publication No. 5-123419.
A sprinkler head of FIG. 9 has a coil spring-like shape-memory alloy 120 at a lower part of a main body 101. When the shape-memory alloy 120 exceeds a predetermined temperature by a fire, the shape-memory alloy 120 restores a preliminarily memorized stretched shape from the coil-spring shape. The restored shape-memory alloy 120 opens a pilot valve hole 110 by pushing up a pilot valve body 112 provided on a valve shaft 111, resisting to a spring 113. Accordingly, the pressure in a room above a piston 108 is lowered to raise the piston 108 so that a rubber packing 114 leaves a valve seat and fire extinguishing water is discharged from a water discharging opening 116.
When the temperature is lowered by the extinguishment of fire by the water discharge, the restoring force to the memorized shape of the shape-memory alloy 120 is lowered so that the pilot valve body 112 is pushed down by the spring 113 to close the pilot valve hole 110. Accordingly, the piston is pushed down by the pressure introduction of the fire extinguishing water from a pilot introduction hole 104 so that the valve seat is closed with the rubber packing 114 to automatically cease the water discharge.
However, in the automatically switchable sprinkler head using a shape-memory alloy as mentioned above, the operation cannot be conducted securely by opening the valve at a predetermined temperature in a fire.
FIG. 10 shows an elastic modulus of a shape-memory alloy with respect to the temperature. The restoring force is proportional to the elastic modulus. The shape-memory alloy is in the crystalline state of a martensite phase. With the temperature rise, it transfers to the crystalline state of an austenite phase. A shape-memory region, which is known as a two phase region, exists therebetween. The shape-memory region has a range in the temperature, for example, of more than several ten degrees.
In order to open a valve in a fire, using the shape-memory alloy 120 having such a characteristic, an operating temperature T1 is determined for starting the water discharge subject to hot air in the fire, and an elastic coefficient G1 corresponding to the operating temperature T1 at the point P is sought. Once the elastic coefficient G1 is sought, the restoring force of the shape-memory alloy 120 having a coil spring-like shape at the operating temperature T1 can be determined so that the force of the spring 113 is set such that the pilot valve body 112 is opened by the restoring force.
Then, the shape-memory alloy 120 is deformed to a stretched memorized shape while being heated at a predetermined operating temperature T1, and contracted to the initial shape before the memorizing operation in an ordinary temperature so as to be assembled as shown in FIG. 9.
However, since the elastic coefficient of the shape-memory alloy increases in the shape-memory region according to the temperature rise as shown in FIG. 10, the restoring force to the memorized shape gradually increases accordingly. On the other hand, the force for opening the pilot valve body 112 fluctuates by the fire extinguishing water pressure introduced into the piston room 109 and the sliding resistance of the valve shaft 111 in addition to the spring 113 force, and thus it has an irregularity to some extent.
Therefore, even if a predetermined restoring force is set by memorizing a stretched shape in the shape-memory alloy 120 at the predetermined operating temperature T1, the restoring force gradually increases according to the temperature rise. With a lowered force for opening the pilot valve 112, the water discharge can be started at a temperature lower than the predetermined operating temperature T1. Or with an increased force for opening the pilot valve 112, the water discharge can be started at a temperature higher than the predetermined operating temperature T1.
As a result, start of the water discharge when it reaches a predetermined operating temperature T1 by hot air in a fire cannot be ensured so that the operating temperature for starting the water discharge cannot be stable, and thus a problem is involved in the lack of reliability. Further, mass production is extremely difficult due to the need of labor in adjusting the shape-memory alloy.
Besides, if the fire extinguishing water is discharged from the water discharging opening 116 with the piston 108 raised in a fire, the water is scattered below the sprinkler head. Therefore, the fire extinguishing water is poured onto a lid 115 so as to cool down the shape-memory alloy 120 by the fire extinguishing water itself, resulting in the termination of the water discharge from the sprinkler head without extinguishing the fire.
Furthermore, if the lid 115 is damaged by the clash of the sprinkler head with a substance, the sprinkler head cannot be operated in a fire.